Add product description (content) to WooCommerce customer processing order email

Add the below code in your functions.php file of your current theme

function render_product_description($item_id, $item, $order){
    $_product = $order->get_product_from_item( $item );
    echo "<br>" . $_product->post->post_content; 

}

add_action('woocommerce_order_item_meta_end', 'render_product_description',10,3);